1. Field of the Invention
The present invention relates to a vane type pump for power steering devices of the kind wherein the eccentricity of the axis of a cylindrical bore formed in a movable member from the axis of a rotor rotating in the cylindrical bore is changed in response to a pressure drop across a throttle which is disposed on a fluid line connecting a pump discharge port with an actuator, for maintaining a constant discharge volume of pressurized fluid.
2. Description of the Prior Art
In known vane type pumps of the aforementioned kind, a pressure chamber defined by an internal surface of a pump housing and an external surface of a movable ring received in the pump housing is divided into first and second pressure chambers. Pressurized fluid compressed by a rotor rotated in the movable ring is led to one of the first and second pressure chambers and is further led through a throttle to an actuator and the other of the first and second pressure chambers. The pressure difference before and behind the throttle acts on the movable ring and causes it to move in the radial direction of the movable ring. This movement of the movable ring changes the eccentricity of the movable ring relative to the rotor, so that the volume of pressurized fluid supplied to the actuator can be maintained constant irrespective of a change in the rotational speed of the rotor.
However, in the known pumps, means for dividing into first and second pressure chambers, the pressure chamber which is defined by the internal surface of the pump housing and the external surface of the movable ring, means for forming the throttle, and means for conducting pressurized fluids in front of and behind the throttle respectively to the first and second pressure chambers are provided separately. This makes the known pumps complicated in construction and high in cost.